Searches for SUSY and Exotics at HERA

1
Searches for SUSY and Exotics at HERA
12th International Conference on Supersymmetry
and Unification of Fundamental InteractionsJune
17-23, 2004 Tsukuba, Japan

• Johannes Haller
• Physikalisches Institut Heidelberg
• now at CERN

(on behalf of H1 and ZEUS)
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Content of the Talk

• HERA I, luminosities and data sets
• DIS at high Q2 and LED
• Leptoquarks
• RP-violating SUSY
• - Resonant Squark Production
• - Bosonic Decays of Stops
• - Sleptons and GMSB
• Single Top Production
• Outstanding Events
• - Isolated Leptons
• - Multi-Electrons
• First Results from HERA II

• Not covered
• Excited leptons and quarks
• General search for new physics
• Contact Interactions
• Finite quark radius
• RP-conserving SUSY
• Doubly charged Higgs
• LFV Leptoquarks
• Magnetic monopols
• Polarized cross-sections
• . . .

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HERA I, Luminosities and Data Sets
e 27.6 GeV
p 920(820) GeV
period collisions vs (GeV) luminosity (pb-1)
93 97 ep 300 40
98 99 e-p 320 20
99 00 ep 320 70

• excellent performance during HERA I
• many new results on searches based on HERA I
  data !
• HERA II data taking on-going (see later)

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SM DIS at high Q2
HERA is a unique facility to test eq interactions
at highest energies !
final HERA I NC/CC cross-section
photon
NC
W boson
CC
test of EW sector up to Q2 40 000 GeV2
? high spatial resolution current HERA limit
on quark radius 0.85 10-16cm
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Large Extra Dimensions
models with LEDs (ADD scenario) cure hierarchy
problem MP2 Rn MS2n MS effective
Planck scale R size of n compact extra
dimensions eq ? eq - virtual KK graviton
exchange interferes with ?, Z0 exchange -
effective contact interaction with coupling ?
1/MS4 expect deviations from SM in NC DIS at
high Q2
Arkani-Hamed, Dimopoulos, Dvali, Phys. Lett.
B429 (1998) 263.
H1, Phys. Lett. B568 (2003) 35. ZEUS, subm. to
Phys. Lett. B, hep-ex/0401009
no significant deviation from SM at high Q2
stat. error dominant !
limit on eff. Planck scale MS gt 0.8 TeV
similar methods allow to set constraints on eeqq
Contact Interactions, finite quark radius, heavy
Leptoquarks
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Leptoquarks

• symmetry between the lepton quark sector in
  the SM
• LQs appear in many extensions of SM
• GUT-like theories, Superstring-inspired
  E6-models, Technicolor-like
• theories, Compositeness models,
• general effective theory BRW model ß(eq)
  0, ½ or 1.

Buchmüller, Rückl, Wyler, Phys. Lett. B191
(1987) 442.
single LQ production at HERA depends on ?
(lepton-quark-LQ coupling)
exploit angular distr. to reduce SM bgr.
topology SM background
e jet NC DIS
? jet CC DIS
?
?
search for resonance in M spectra
e jet
for both ejet and ?jet
no resonance observed in full HERA I data set
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Leptoquarks Exclusion Limits
BRW model ß fixed
example S0,L ß(eq) ß(?q) 0.5
Tevatron LQ pair production, independent of
?. LEP t-channel LQ contribution to hadr.
cross-section, strongly dependent on ?.
H1, prelim., EPS03 ZEUS, Phys. Rev. D68 (2003)
052004
generic LQ models ß free
D0

• HERA limits
• dependent on ?
• independent of ß(eq)
• stringent for
• small ß(eq)

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Resonant Production of Squarks
general superpotential has RP-violating terms
For proton stability ?? 0 sufficient

• main consequences for colliders
• fundamental instability of SUSY matter (LSP
  decay) ? indirect
  sensitivity to ?, ?, ? from sparticle pair
  production
• resonant production of sparticles at colliders.

HERA single squark production via ?1jk
ep, e-p all flavors can be probed e.g.
stop production via ?131 in ep collisions
best discovery reach for SUSY at HERA
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Squarks Decay Modes
? ? 0 opens a large variety of squark decay
modes.
LSP decay
RP-violating decay
example of gauge decays
many final states considered to reduce dependence
on SUSY parameters (e.g. µ, tanß, M2, ?,
Msquark, ) ? BRtot 1
all channels in agreement with SM expectation
H1, subm. to Eur. Phys. J. C, hep-ex/0403027
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Squarks Exclusion Limits
constraints on ?(Msquark) e.g. third generation
(j3, k3)
stop
sbottom

• For ?0.3 (e.m. strength) squarks up to 280 GeV
  are ruled out
• small couplings improvement of indirect
  low-energy limits

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Squarks mSUGRA Interpretation
HERA limits follow squark isomass curve for ?
0.3 squark masses up to 275 GeV ruled
out HERA sensitivity comparable with LEP and
Tevatron bounds
L3 (tanß2)
D0 (j1,2)
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Events with Isolated Leptons
H1 observes excess of spectacular events

• isolated e or µ with high pT
• pT,miss
• jet with high pT

main SM contribution from W production
H1 e µ
e/-
p
pThad (GeV)
not confirmed by ZEUS
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Events with Isolated Leptons

• t search performed by ZEUS
• selects isolated taus decaying to
  hadrons
• pencil-like jets

3 events found, 0.40 0.13 exp.
ZEUS t?had.
not confirmed by a preliminary H1 analysis
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Events with Isolated Leptons
current situation observed /expected
H1 electron muon tau (prelim)
pTX gt 25 GeV 5 / 1.8 0.3 6 / 1.7 0.3 0 / 0.53 0.10
pTX gt 40 GeV 3 / 0.7 0.1 3 / 0.6 0.1 0 / 0.22 0.05
ZEUS electron muon tau
pTX gt 25 GeV 2 / 2.9 0.6 5 / 2.8 0.2 2 / 0.20 0.05
pTX gt 40 GeV 0 / 0.9 0.1 0 / 0.9 0.1 1 / 0.07 0.02

• interpretation unclear
• need more data from HERA II

H1, Phys. Lett. B561 (2003) 241. ZEUS, Phys.
Lett. B559 (2003) 153. H1, prelim.,
DIS04 ZEUS, Phys. Lett. B583 (2004) 1.
e/m tau
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Bosonic stop Decay
possible SUSY explanation of isolated leptons
T. Kon et al, Mod. Phys. Lett. A12 (1997) 3143.

1. sbottom is significantly lighter than stop
2. decay to gauginos kinematically forbidden

signature 3 jets pT,miss jet l
pT,miss
H1 j e pT,miss j µ pT,miss j j j pT,miss e j
data 3 8 5 1100
SM exp. 3.8 0.9 2.7 0.5 6.2 1.7 1120 131
excess in jµpT,miss not confirmed by other
channels
H1, subm. to Phys. Lett. B, hep-ex/0405070
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Bosonic stop Decay Interpretation
allowed signal cross sections (s?s)
excluded (Mstop,Msbottom) area
all channels (except jµpT,miss ) consistent with
non-observation
stops up to 275 GeV excluded for ?1310.3
? Isolated lepton events can hardly be
interpreted as scalar tops.
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RP-viol. SUSY with Sleptons and Gravitinos
if Msquark gtgt Mslepton ? can still be probed
via slepton exchange
RP-violation GMSB
signature isolated ? pT,miss jet
no deviation from SM obs. 1 exp. 3.1 0.3
H1, prelim., DIS04
analogous
recall isolated leptons
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Production of single top Quarks
another possible explanation of isolated leptons
H1, Eur. Phys. J. C33 (2004) 9. ZEUS, Phys.
Lett. B559 (2003) 153. and add. DESY-03-188
FCNC couplings to top quark (?tu?,?tuZ)
exclusion limits
dedicated searches performed at HERA
leptonic channels

• isolated lepton events
• ET,miss lepton jet

• no deviation from SM
• low sensitivity due to
• QCD background

hadronic channel
exp. reach of HERA II
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Observation of Multi-Electron Events
search for events with several leptons in final
state
e H1, Eur. Phys. J. C31 (2003) 17. ZEUS,
prelim., ICHEP02
good agreement with SM found in muon and tau
channels
mu H1, Phys. Lett. B583 (2004) 28. ZEUS,
prelim., ICHEP02
tau H1, prelim., DIS04
excess observed in electron channel at high
invariant mass
main SM contribution from ?-? collisions
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Observation of Multi-Electron Events
excess in multi-electron channel at high
invariant mass
3e
2e
M12 mass of two highest pT electrons
event numbers in electron channel
observed/expected
selection H1 (115 pb-1) ZEUS (130 pb-1) prelim.
2e, M gt 100 GeV 3 / 0.30 0.04 2 / 0.77 0.08
3e, M gt 100 GeV 3 / 0.23 0.04 0 / 0.37 0.04
need more data
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First Results from HERA II
background problems are solved !
H1, prelim., DIS04

• HERA runs with 3 times higher luminosity
• expected 700 pb-1 by mid 2007
• Pe up to 50 achieved

based on 17 pb-1
multi-electrons
data SM exp.
2e 10 15.8 1.7
3e 2 3.0 0.4
isolated leptons
integrated Luminosity
pTX gt 25 GeV
e µ
data SM exp.
e 2 0.34 0.07
µ 0 0.29 0.08
more data from HERA II needed
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Conclusion

• HERA is a unique facility to search for new
  physics.
• A large variety of searches for SUSY and exotics
  has been performed with HERA I data (CI, LED,
  single top, finite quark radius, excited leptons,
  excited quarks, leptoquarks, resonant squark
  production, bosonic stop decay, magnetic
  monopoles, LFV, ...).
• Outstanding events have been observed (isolated
  leptons, multi-electrons). More data are needed
  for clarification.
• Background problems after the HERA II upgrade are
  solved.
• The high luminosity runs of HERA II have started.
  
• 700 pb-1 are expected by mid 2007.
• First results from HERA II are available now,
  more to come !